The youngster also becomes the fourth most expensive defender in world football.

World's most expensive defenders

Player

From

To

Amount (£m)

Date

David Luiz

Chelsea

Paris St-Germain

40

2014

Thiago Silva

AC Milan

Paris St-Germain

36

2012

Rio Ferdinand

Leeds United

Manchester United

33.1

2002

Luke Shaw

Southampton

Manchester United

27

2014

Marquinhos

Roma

Paris St-Germain

27

2013

Fabio Coentrao

Benfica

Real Madrid

27

2011

Pepe

Porto

Real Madrid

25

2007

Southampton insist the money they have received from United will be reinvested in the team.

"While we are sad to see Luke depart the club, we fought to ensure that we got the right deal for a player in whom we have invested a great deal of work over the past decade," said executive director Les Reed.

"This deal is a good one for Southampton Football Club and hopefully sends a clear message to other clubs wishing to bid for our players.

"Luke's transfer fee will be reinvested into the team as our new manager, Ronald Koeman, builds for the new season and for years to come."